웨이블릿 변환 기반의 Wavelet-OFDM 시스템과 푸리에 변환 기반의 OFDM 시스템의 성능 비교

왈시-하다마다 변환(Walsh-Hadamard Transform, WHT)을 적용한 OFDM(Orthogonal Frequency Division Multiplexing) 변조방법은 시스템의 PAPR(Peak-to-Average Power Ratio)을 줄여주고, 시스템의 BER(Bit Error Rate) 성능을 향상시키는 장점이 있다. 그러나 기존의 이러한 왈시-하다마다 변환에 기반한 OFDM 시스템은 여전히 비교적으로 높은 PAPR문제가 있다. 그러므로 본 논문에서는 DGT(Data Grouping Technique)이라고 부르는 기술을 제안하고, 이 기술과 왈시-하다마다 변환 기술을 적용하여 PAPR을 더욱 줄여주는 OFDM 시스템을 설계한다. 제안한 DGT기술은 WHT-OFDM뿐만 아니라 일반 OFDM에서 PAPR을 줄여주는 방법들 중에서 큰 단점이 되는 부가정보(side information)가 성능에 대해 독립성을 가진다는 특징이 있다. 컴퓨터 시뮬레이션을 통해 제안한 시스템의 유용성을 검사하고 성능을 검증하였다. The conventional OFDM (Orthogonal Frequency Division Multiplexing) modulation can be combined with WHT (Walsh-Hadamard Transform) to reduce PAPR (Peak-to-Average Power Ratio) and improve BER (Bit Error Rate) performance. However, this WHT-based OFDM system still suffers a relatively high PAPR. Therefore, we suggest a new technique, called DGT (Data Grouping Technique) and design an OFDM system employing it and WHT to further decrease PAPR without the BER performance degradation. h salient property of DGT is the independence of the side information which is inherently a principal drawback of the well-known PAPR reduction techniques for OFDM system as well as WHT-based OFDM. The simulation programs have been also performed to verify the validity of the proposed system.

Orthogonal Frequency Division Multiplexing (OFDM) is one of the promising contendents in the race of very high data rate delivery, for 4G wireless systems. The conventional OFDM systems, so far deployed make use of Fast Fourier Transform (FFT) as their basic building block. Besides the numerous advantages, the restriction over the data rate imposed by the FFT in the form of cyclic prefix may be intolerable for the next generation OFDM systems. So, researches are on the way to replace FFT with a more suitable transform which is redundant free. DWT OFDM is one such system in which FFT in the conventional OFDM is replaced with Discrete Wavelet Transform (DWT). Using simulations, already it has been established that in ideal conditions, the performance of DWT OFDM is better than that of FFT OFDM. As phase noise can be considered as the major RF impairment and one of the leading performance limiting factors of the wireless systems, this paper analyses the Bit Error Rate (BER) performance of the DWT OFDM in presence of phase noise. BER performances of both DWT OFDM and FFT OFDM are analysed and compared in presence of phase noise. For this, Matlab Simulink model have been developed for both types of OFDM, and simulation is carried over in presence of phase noise for different modulation schemes. In all cases the BER performances of DWT OFDM is found to be fairly ahead that of FFT OFDM.

Conventional orthogonal frequency division multiplexing (OFDM) system utilizes cyclic prefix (CP) to remove the channel-induced inter-symbol interference (ISI) at the cost of lower spectral efficiency. In this paper, a generalized sidelobe canceller (GSC) based equalizer for ISI suppression is proposed for uplink multi-antenna OFDM systems without CP. Based on the block representation of the CP-free OFDM system, there is a natural formulation of the ISI suppression problem under the GSC framework. By further exploiting the signal and ISI signature matrix structures, a computationally efficient partially adaptive (PA) implementation of the GSC-based equalizer is proposed for complexity reduction. The proposed scheme can be extended for the design of a pre-equalizer, which pre-suppresses the ISI and realizes CP-free downlink transmission to ease the computational burden of the mobile unit (MU). Simulation results show that the proposed GSC-based solutions yield equalization performances almost identical to that obtained by the conventional CP-based OFDM systems and are highly resistant to the increase in channel delay spread.

This article presents a novel peak-to-average power ratio (PAPR) reduction scheme based on the insertion of dummy random Gaussian (IDRG) subcarriers to the data constellation points in the frequency domain integrated with a partial transmit sequence (PTS) technique. The dummy signals are Gaussian random signals which have the same statistical distribution as that of the output signals of the conventional orthogonal frequency division multiplexing (OFDM) system. The integration of IDRG with PTS technique reduces the overall complexity of the OFDM system. Compared to the conventional PTS which requires several inverse fast Fourier transform (IFFT) operations, the proposed IDRG–PTS scheme requires only half as many IFFT operations with comparable PAPR performance. Simulation results have been examined with 16 quadrate amplitude modulation OFDM signals.

Orthogonal Frequency Division Multiplexing (OFDM) system is used for the reducing almost every kind of interference in any communication system. For designing OFDM system need to use FFT and IDFT phenomena of signal processing, in this work mainly concern to improve peak to average power ratio for this system because this system is multicarrier system, and in the multiple carriers are nearly having same frequency but still they do not overlap to each other because these multiple carriers are orthogonal to each other. These multiple carriers have different power and energy levels so we get very unfair PAPR for this system here channel codes can be use to improve PAPR for that system, so in this work we will focus on the Comparing PAPR of OFDM system for different Channel codes.

SUMMARY The main disadvantage of orthogonal frequency divisionmultiplexing (OFDM) is the high time domain PAPR. The larger PAPRsignal would fatallydegrade BER performance in non-linear channels. Thispaper proposes an improved DSI method, which can achieve better PAPRand BER performances in the non-linear channel with less computationcomplexity than the conventional DSI method. The feature of proposedmethod is to employ the time-frequency domain swapping algorithm inthe determination of frequency data for dummy sub-carriers. This paperpresents various computer simulation results to verify the effectiveness ofproposed DSI method. key words: OFDM, PAPR, dummy sub-carriers, non-linear amplifier 1. Introduction The OFDM technique has been received a lot of attentionespecially in the field of wireless communications becauseof its efficient usage of frequency bandwidth and robustnessto multi-path fading. One of the limitations of using OFDMtechnique is the larger peak to averaged power ratio (PAPR)of its time domain signal [1]. The larger PAPR signal wouldcause the severe degradation of bit error rate (BER) perfor-mance due to the inter-modulation noise occurring in thenon-linear amplifier.To overcome the PAPR problem in OFDM systems,various PAPR reduction methods for OFDM signal havebeen proposed including the selected mapping method(SLM) [2], partial transmit sequence method (PTS) [3] anddummy sequence insertion method (DSI) [4]. All of thesemethods improve the PAPR performance by controlling thephase of data or dummy sub-carriers. The SLM and PTSmethods control the phase of data sub-carriers and the DSImethod controls the phase of dummy sub-carriers. First twomethods are required to inform the phase information con-trolled for the data sub-carriers to the receiver as the sideinformation. Since the side information is required to trans-mit separately from the data information through the data orcontrol channels with the higher signal quality for the cor-rect demodulation of data information at the receiver, the

In this paper, a novel scheme of the weighted distortion-to-signal ratio (WDSR) based partial transmit sequence (PTS) is proposed to enhance the bit error rate (BER) performance in nonlinear distorted orthogonal frequency-division multiplexing (OFDM) systems, and its key idea is to employ the WDSR metric to predict the nonlinear distortion caused by high power amplifier (HPA). Furthermore, several alternative signals can be generated by the PTS technique, and the signal with the minimum WDSR is selected as the transmitted OFDM signal. Since the WDSR metric predicts the nonlinear distortion of OFDM systems, the BER performance of nonlinear distorted OFDM systems can be significantly improved. Simulation results show that the proposed WDSR-PTS scheme offers better BER performance than the conventional peak-to-average power ratio (PAPR) based PTS scheme.

Orthogonal frequency division multiplexing (OFDM) system has been widely used for the high speed digital communication area and it is very promising for the next generation communication standard because of high data rate capability. However, OFDM system has inherent serious problem of high peak-to-average power ratio (PAPR) that makes the OFDM signal be distorted in the nonlinear HPA (high power amplifier). In this paper, CI (carrier interferometry)-OFDM system is considered to overcome this problem and is newly analyzed in the selective fading and narrow-band interference channel. CI-OFDM system distributes each parallel data to all sub-carriers in differently phase-rotated form. So, PAPR becomes lowered and it shows the frequency diversity effects. BER (bit error rate) performance is analyzed in the selective fading and narrow-band interference environment. From the simulation results, it is confirmed that CI-OFDM system calms down the high PAPR problem and CI-OFDM system is more robust than the ordinary OFDM system in the selective fading and narrow-band interference channel.

This work deals with the enhancement of one of the main techniques that is used widely in number of communications systems these days; Orthogonal Frequency Division Multiplex (OFDM). Its powerfulness comes from improving the system's data rates even under harsh channels conditions by making use of the Inverse Fast Fourier Transform (IFFT) idea. However, it suffers from different drawbacks, which make it intrinsically obstinate, such as the Peak-to-Average Power Ratio (PAPR) and synchronization issues. Thus, an analysis of an alternative work will be provided in this work based on the wavelet transforms; wavelet packet transforms-based Daubechies 4 will be analyzed and compared to our previously published work in order to increase the OFDM-based work flexibilities. This comparison will be based on the bit error rates (BER) and exceeding the PAPR values a certain threshold. A MATLAB simulation has been performed in order to verify the reliability of the proposition in order to replace the FFT stage in the OFDM. As a result, the WPT work gives a 1 dB enhancement over the conventional OFDM at 10−3 probability, while the previously Haar based published work enhances this value by 8.8%. in addition to enhances the BER reliability over the proposed RoF channel link.

Based on superposition of signals in the time domain, we propose a new low-complexity scheme for the reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. The proposed scheme first generates signal candidates by combining an OFDM signal and its cyclically delayed versions with different delays and phases, and then selects the candidate signal with minimum PAPR. It is shown that the complexity of the proposed scheme is significantly lower than that of the selective mapping (SLM) at the cost of some degradation in the bit error rate (BER) performance and, at similar PAPR and coded BER performance, is lower than that of the low-complexity SLM proposed recently.

In this paper, we design and evaluate the wavelet-OFDM (wavelet orthogonal frequency division multiplexing) system based on wavelet transform. Wavelet transform has functions other than the Fourier transform using sine and cosine functions as well as the number of wavelets. In addition, various wavelets are used for wavelet transformation, and the change of signals according to the wavelets can be confirmed. In the conventional CP-OFDM (cyclic prefix orthogonal frequency division multiplexing), inverse fast fourier transform (IFFT) is used. In the wavelet-OFDM system, inverse discrete wavelet transform (IDWT) is used. Therefore, this study confirms bit error rate (BER), peak to average power ratio (PAPR) and OOB (out of band) characteristics of the two systems through simulation results. Comparing the characteristics of the conventional OFDM and the wavelet-OFDM, the same BER performance is shown. However, it can be confirmed that the wavelet-OFDM has lower PAPR performance than that of the conventional OFDM, and OOB is also lower than that of the conventional OFDM.

In response to the inefficiency of power amplifier in conventional Orthogonal Frequency Division Multiplexing (OFDM) system, a low Peak-to-Average Power Ratio (PAPR) scenario can be obtained by implementing several PAPR reduction techniques. Partial Transmit Sequence (PTS) is a well-known instance to provide zero distortion for the system, while clipping is one of the simplest methods but it is sacrificing the error rate performance. In this work, Authors focused on analyzing the implementation of PTS and Palm Date Leaf clipping technique on OFDM system with 16-, 64-, 256-, and 1024-QAM under various Nakagami channel. In addition, the High-Power Amplifier (HPA) was also considered by using Solid State Power Amplifier (SSPA) model. It was found that linear HPA serves as the lower boundary for non-linear HPA, and system under high saturation level performs similarly. In physical properties, high saturation level is equivalent to higher power consumption in amplifier. Thus, optimal level was obtained by considering taking the one with moderate BER performance. After the system’s PAPR was reduced, the optimum saturation level of HPA was found to be 5 dB, 8 dB, 9 dB, and 11 dB for each Quadrature Amplitude Modulation (QAM) under Nakagami channel with m value of 1.5. However, this value was found to be ample for lower m value such as 1 or 0.7. In this case, the system required lower saturation level on the HPA for Nakagami channel with lower m value.

High Peak to Average Power Ratio (PAPR) in the transmitted signal is still a very important challenge in Orthogonal Frequency Division Multiplexing (OFDM) systems. In this paper, we present a new Zadoff-Chu matrix Transform (ZCT) precoded Selected Mapping (SLM) based OFDM (SLM-OFDM) system for PAPR reduction. The proposed system is based on precoding the constellation symbols with ZCT precoder after the multiplication of phase rotation factor and before the Inverse Fast Fourier Transform (IFFT) in SLM-OFDM Systems. At the clipping probability of 10−3, simulation results show that our proposed system can reduce the PAPR up to 5.0 dB with N=64 (System subcarriers) and V=16 (Dissimilar phase sequences) for QPSK modulation. Additionally, ZCT based SLM-OFDM systems also take advantage of frequency variations of the communication channel and can also offer substantial performance gain in fading multipath channels.

The authors propose a novel localised discrete Fourier transform (DFT) spread M-ary amplitude shift keying (M-ASK) orthogonal frequency division multiplexing (OFDM) system with the Hermitian symmetry (DFT-spread M-ASK HS OFDM) to reduce the peak-to-average power ratio (PAPR). Compared with the conventional OFDM and localised DFT-spread OFDM, the proposed system has lower PAPR not only because of the DFT-spread scheme but also its lower modulation order than other OFDM systems. The lower modulation order of the proposed system can be achieved by using the Hermitian symmetry of DFT. The simulation result shows that the localised DFT-spread M-ASK HS OFDM provides a significant improvement in bit-error-rate and reduced PAPR.

There have been a set of conversion matrices proposed recently by Wang and Ouyang to simplify the inverse fast Fourier transform (IFFT) computation involved in the selected mapping (SLM) scheme for reduction of the peak-to-average power ratio (PAPR) in orthogonal frequency division multiplexing (OFDM) systems. As compared to the conventional SLM scheme, the modified approach achieves close PAPR reduction with much lower complexity but degraded bit error rate (BER) performance. In this paper, we propose a new set of conversion matrices for the SLM scheme such that the complexity can be reduced without sacrificing the BER performance. It is shown that the improved SLM method has better BER performance and lower complexity than the previous work by Wang and Ouyang, at the cost of a slight PAPR reduction loss.